In electron beam lithography systems such as the system described in U.S. Pat. No. 4,390,789 (Smith et al), an electron beam is scanned to effect movement of the beam spot in a target plane. In the Smith et al system, in particular, the primary purpose of scanning the beam spot is to directly write circuit patterns on a reticle or semiconductor target wafer as part of the fabrication of microcircuit devices. In order to control beam deflection a relatively large amount of data, describing the pattern features to be written, must be prepared and supplied to the system. The preparation of such detailed data, describing substantially every point in the pattern to be traced, is quite time consuming. Moreover, the data processing is relatively complex, as well as time consuming.
A prior art approach to simplifying the input data requirements and resulting complexity of electron beam lithography svstems is described in U.S. Pat. No. 4,433,384 (Berrian et al). In that system, data describing the various circuit patterns to be written are subdivided into blocks of segment figure data and stored in a pattern data memory. Multiple pattern generators, each including a bit map memory, simaltaneously convert blocks of segment figure data into bit maps and store these bit maps in respective bit map memories. The bit maps are then used to provide continuous beam blanking data during a complete scan of the target area. The resulting system permits higher speed operation than was possible in prior art systems. However, input data for the system is still relatively complex. More importantly, the blanking approach requires the system to take the time required to scan the entire target area, even though the beam is selectively blanked during such scan under the control of the bit map. In other words, the beam must execute a complete raster scan, line by line, and is selectively blanked under the control of the derived bit map.